This is the actual time when the parent was physically present in the United States, not simply as a resident. This means that any travel outside the United States, including vacation, should be excluded. Evidence or proof of physical presence/residence is required. This can be demonstrated by providing documents such as school transcripts, W2 (tax returns). The consular officer will determine whether or not you have met the requirements and demonstrated adequate physical presence.
Note: Any periods of time spent overseas with the United States military/government etc. may be computed as physical presence in the United States for transmission of citizenship purposes. Time spent as a dependent of a United States military/government employee may also be computed as physical presence. Military records may be requested.